Method for verifying age-depth relationships of rock in sedimentary basins

ABSTRACT

Method for verification of age-depth relationships of rocks in sedimentary basins by reconstructing the subsistence rate of samples, in which, by determining the precipitation depth and precipitation temperature of a carbonate precipitation, wherein by determining the precipitation depth and the precipitation temperature of the carbonate precipitation in the geological-history-determining sedimentary rocks, from which a sample is taken, a set point is fixed.

The invention relates to a method for the verification of age-depthrelationships of rocks in sedimentary basins according to the preambleof the main claim. This verification can be used in general in the fieldof oil and gas exploration. In particular, the invention provides amethod for validation and calibration of mathematical models ofsedimentary basins (sedimentary basins such as the North German Basin).

Sedimentary basins are those regions in which the earth's crust subsidesdue to sediment deposition. Sediment eroded from the continents istransported by rivers or ocean currents and is deposited in them. Newsediment layers are continuously deposited one on the other, causing thebasin to fill and the earth crust to be pressed into the mantle.

In sedimentary basins, large amounts of organic matter are stored, whichcan be converted to natural gas and oil in geological time periods dueto the effect of temperature and pressure. A crucial parameter for theexploration of natural gas or petroleum is the knowledge of the depth ofthe oil-bearing strata. By way of example, most of the oil being pumpedtoday came from the Jurassic age. This layer is now, of course, nolonger at the surface but has been moved to a certain depth below theearth surface (about 1 to 2 km) by the overlaying of layers of youngerdeposits. The oil deposit to be pumped, since it is lighter than water,collects higher up in the Jurassic layer. It is therefore important toknow where the “Jurassic” is below the surface, and the general trend ofthe vertical downward movement, but in certain cases also the upwardmovement, over time. This can be described in an age-depth relationship,which can be represented in a diagram in which the depth of the rocklayer below the earth's surface is shown as a function of time. Thisage-depth relationship is determined using mathematical modeling,so-called basin models.

A basin model is a discrete mathematical representation of a geologicbasin in the form of a plurality of cells that form a mesh network(finite elements). The simulator model of a basin makes it possible tocalculate in each cell a certain number of parameters. The aim of basinmodeling is to produce an age-depth relationship for the sedimentarybasin, from which then the location of certain oil- and gas-carryinglayers, can be predicted as a function of time or period. Based on thisprediction decisions are made, as to whether the so-called sinking ofexploratory drillings is successful or not. The cost of drilling arehigh, so that accurate predictions of the basin models are an importantimputed items in oil or gas-exploration.

The publication EP 1435429 A1 discloses a method and a system fortime-delayed analysis of cause and effect of changes in a wellboreinterval, wherein a first log data is detected with a logging sensorduring a first pass through the wellbore interval and a second log datais acquired by the logging sensor during a second pass over the wellboreinterval at a time later than the first log data, a plurality of deltavalues are calculated between the first log data and the second logdata, an observed effect is derived using the delta values andsubsequently a correlation between the observed effects and a causalevent is identified, and the correlation is displayed on a displaydevice.

The difficulty in basin modeling is that there may be considerableindividual differences from basin to basin due to tectonic movements andother geological processes. The individual mathematical modeling of asedimentary basin, also for determining the relative vertical movementof a layer, in a basin taking into account all factors of variousmagnitudes influencing subsidence has not yet been solvedsatisfactorily.

To increase the accuracy and veracity of basin models, it wouldtherefore be advantageous if “fixed points” were known for a basin andits basin model, which enable establishment of an age-depthrelationship, regardless of the basin model, and thus to validate andcalibrate the basin models with an independently created age-depthrelationship.

It is the object of the invention to provide a method which makespossible a verification of the age-depth relationships determined by anymeans, for validation and possibly calibration of sedimentary basinmodels by determining an age-depth relationship.

The inventors have discovered that the object of the invention can besolved when a method is used to determine the age-depth relationship,which is comprised of e.g. the following steps:

-   -   i. dissolution of the precipitated calcium carbonate from        sedimentary rocks by use of dilute acids (→ Solution A),    -   ii. determination of the Ca isotope ratio of the two most common        isotopes ⁴⁰Ca and ⁴⁴Ca (⁴⁴Ca/⁴⁰Ca) or even another Ca—isotope        ratio for the determination of the isotope ratio of the        precipitated CaCO₃ (CC). The ratio may be indicated in the delta        notation customary in isotope geology (δ^(44/40)Ca_(cc)).    -   iii. calculating the Ca isotopic difference (Δ^(44/40)Ca)        between the solution (BS=Bulk Solution) and the CaCO₃ (CC)        precipitated from the solution according to        (Δ^(44/40)Ca=δ^(44/40)Ca_(CC)-δ^(44/40)Ca_(BS)) if        δ^(44/40)Ca_(BS) is known. Otherwise, first determine the        δ^(44/40)Ca_(BS)-value.    -   iv. determining the CaCO₃ precipitation temperature across the        relationship Δ^(44/40)Ca (‰)=0.02 (‰/° C.)*temperature (°        C.)−1.46‰ (Gussone et al. 2004) according to Equation 1.

$\begin{matrix}{{T\left( {{^\circ}\;{C.}} \right)} = \frac{{\Delta^{44/40}{Ca}} + 1.46}{0.02}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

-   -   V. determining the CaCO₃ precipitation depth (X in meters (m))        is determined using Equation 2.

$\begin{matrix}{{X(m)} = \frac{{\delta^{44/40}{Ca}_{CC}} - {\delta^{44/40}{Ca}_{BS}} + 1.16}{0.00066}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

If δ^(44/40)Ca_(BS) is not known, then the following steps arenecessary:

-   -   a) separation and recovery of strontium ions (Sr²) from solution        A, for example, by on chromatography.    -   b) determination of Sr isotope ratio ⁸⁷Sr/⁸⁶Sr or another        strontium isotope ratio of the separated strontium ion (Sr²⁺).    -   c) determining the age of the sample by comparing the measured        ⁸⁷Sr/⁸⁶Sr-isotope relationship with the known Sr isotope ratio        of Phanerozoic sea water (FIG. 2).    -   d) determining the δ^(44/40)Ca_(BS) based on known correlations        (FIG. 3).

Then proceed with step iv.

It may be beneficial if prior to the determination of the Ca isotoperatio (step ii) a solution of known isotopic composition Ca (spikesolution) is added for calibration.

The dissolution of the precipitated calcium carbonate from sedimentaryrocks by means of dilute acids (step i) should be done with a weakorganic or inorganic acid, e.g. formic acid or 2N HNO₃ to ensure that nocalcium is leached from the non-calcium carbonate host rock, i.e., it ismade sure that the original calcium isotopic composition of the calciumcarbonate precipitated from the rock can be measured. The skilled workeris familiar with suitable acids and their strengths.

The inventors were first to recognize that the phenomenon oftemperature-dependent calcium isotope fractionation during theprecipitation of calcium carbonate (CaCO₃) in porous rocks can beexploited to determine an empirical age-depth relationship.

From the context of precipitation temperature (T_(precipitation)), depthand geogenic temperature increase as a function of depth an empiricalage-depth relationship can be determined for several depths (fixedpoints). These values can then be compared with the basin modelcalculated theoretical values. These fixed points enable calibration ofbasin models which can lead to an improvement in the identification ofoil-bearing strata and savings in drilling costs.

With the maturation of the oil, large amount of methane (CH₄) andpossibly carbon dioxide (CO₂) are produced, which rises in the rockstrata and reacts with the sea water still existing in the rock (mostlyfrom the Jurassic sea, but also waters from other epochs) and convertsthe therein dissolved calcium to calcium carbonate (CaCO₃). This takesplace in a certain depth above the oil-bearing strata, which is uniquelycharacterized by pressure and in particular temperature. In particular,the T_(precipitation) is defined by the geogenic gradient with atemperature increase of ˜0.033° C./m (the rule of thumb here is anincrease of 3° C. per 100 m depth in the earth). In other words, atabout 100 m depth, the temperature is about 3.3° C. higher than at thesurface. The actual temperature at 100 m depth is then obtained from theaverage temperature at the surface of ˜15° C. and the geogenic increase(T_(precipitation)) of 3.3° C., i.e., one can presume a temperature inthe order of ˜18.3° C. (T_(geogenic)=15° C. (0.033° C./m)*Depth (m)) ata depth in the earth of 100 m. The geogenic, increase of temperaturewith depth is a rule of thumb that can vary within a certain statisticalframework. The actual temperature profile in a sedimentary basin can becorrected by the direct temperature measurements in a wellbore.

Regardless of the geogenic connection T_(precipitation) can bereconstructed by the measurement of a specific Ca-isotope ratio (here:⁴⁴Ca/⁴⁰Ca). When comparing T_(precipitation) with T_(geogenic) it isfound that as a rule T_(precipitation) is always less than T_(geogenic)(T_(precipitation)<T_(geogenic)). This is because the increased drilleddepth where the rocks are drilled today and of course a highertemperature than the corresponding depth at which the calcium carbonateprecipitation took place, usually many millions of years earlier.

The Ca isotopy of calcium carbonate (CaCO₃, calcite and aragonite) istemperature dependent, in the manner, that for kinetic reasons thenegative Ca isotopic difference between the solution (BS=Bulk Solution)and the CaCO₃ (CC) precipitated from the solution as function oftemperature (see equation) keeps getting smaller.Δ^(44/40)Ca=δ^(44/40)Ca_(CC)−δ^(44/40)Ca_(BS)

According to the following equation Δ^(44/40)Ca (=fractionation factor)is relatively large for low and small for higher temperatures. Theisotopic equilibrium (equivalent value of CC and BS) is reached inaccordance therewith at a temperature of approximately 73° C., at whichthere is no more isotopic difference between BS and CC. A temperaturereconstruction is therefore only possible in the temperature interval to≦73° C.T(° C.)=Δ^(44/40)Ca+1.46)/10.02

The equation is true for temperatures <73° C.˜(Δ^(44/40)Ca=0).Δ^(44/40)Ca is expressed in per mil (‰).

Assuming the general geothermal gradient of 0.033° C./m and an averagetemperature at the surface of approximately 15° C., then thetemperature-dependence of the Ca isotope can be converted into adepth-dependence, according to the following equation. This means thatif there is a CaCO₃ precipitation in the geological depth, theΔ^(44/40)Ca isotope value clearly reflects the geological depth andtemperature, making it thus possible to reconstruct the geologicalsubsidence rate and history.Δ^(44/40)Ca(m)=└15+0.033·X(m)┘·0.02−1.46

For temperature determination with CaCO₃ precipitation here is needed,besides the Ca isotopic composition of the precipitated CaCO₃precipitation (δ^(44/40)Ca_(CC)), also an indication of the Ca isotopiccomposition of the parent solution (δ^(44/40)Ca_(BS)) is required. Therelationship between precipitated CaCO₃ (CC) (δ^(44/40)Ca_(CC)), theparent solution BS (δ^(44/40)Ca_(BS)), the geothermic gradient and thedepth X(m) in the earth's crust during CaCO₃ precipitation can bedetermined byδ^(44/40)Ca_(CC)=[15+0.033·X(m)]·0.02−1.46+δ^(44/40)Ca_(BS)

To Equation 2

$\begin{matrix}{{X(m)} = \frac{{\delta^{44/40}{Ca}_{CC}} - {\delta^{44/40}{Ca}_{BS}} + 1.16}{0.00066}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

FIG. 1 shows graphically the relationship between the Ca-isotopefractionation, the temperature (T) and the depth (X).

For the determination of δ^(44/40)Ca_(BS) the calcium isotopiccomposition of the parent solution (BS) must be known, such as by seawater of the corresponding geological depositional environment. If nooriginal solutions are any longer present, the age of the parentsolution, from which the carbonates have precipitated, can be determinedby a determination of the ⁸⁷Sr/⁸⁶Sr isotope ratios of the strontium ions(Sr⁺⁺) extracted from the sedimentary rock and the comparison with thePhanerozoic ⁸⁷Sr/⁸⁶Sr-seawater curve. Such a ⁸⁷Sr/⁸⁶Sr-seawater curve isshown in FIG. 2.

If the age of he parent solution is known, then the δ^(44/40)Ca_(BS) acan be read from FIG. 3.

The (CaCO₃) precipitation temperature and depth of the precipitatedCaCO₃ is then obtained according to Eq. 2.

The determination of Ca and Sr isotope ratio can take place with thehelp of mass spectrometry (MS). In the following, this method will beexplained in more detail by way of example, with the aid of which themethod of the invention can be performed, the person of ordinary skillwill, in certain cases, make changes to individual process parameters inthe manner known to him.

The eluate, which contains substantially only the calcium, isconcentrated to about 1 μl and applied to an approximately 1 mm wide andrhenium wire, the so-called filament. This sample is then mounted in thethermal ionization unit of a mass-spectrometer. After the ionizationunit is evacuated and the pressure therein is lower than 10-6 mbar, thefilament is gradually heated until it becomes red hot. Thereby thecalcium on the filament and its isotopes ⁴⁰Ca and ⁴⁴Ca is thermallyevaporated and ionized. The evaporated ions enter into an appliedelectric field with an accelerating voltage of about 10,000 volts. Theaccelerated ions, which must pass different ion-optical lenses, reachingmagnets which provide, on the basis of the mass-dependent equilibrium ofthe Lorentz force and the centripetal force, for a splitting of the ionbeam. The lighter ions (here ⁴⁰Ca) fly a tighter radius than the heavierions (here ⁴⁴Ca). After passing the magnet, the ions hit detectionunits, the so-called Faraday beaker, where the ions are slowed down by aconductive or guiding layer. The ions generate an electrical current inthis beaker, which flows through a high-impedance resistor (˜10¹¹ ohms)and generates a relatively high electrical voltage, which can be easilymeasured. This is done individually for each ion, so that for evaluatingintensity one can evaluate the measured voltage. The number of ionsflowed then is obtained from the ratio of the masses, since the voltageis directly proportional to the flowed ions per time. The evaluation iscomputer-assisted via a known algorithm.

After measuring the δ^(44/40)Ca and ⁸⁷Sr/⁸⁶Sr-values the followingparameters of the sample are now known:

-   -   1. The temperature during the time of precipitation        (T_(precipitation)) of CaCO₃ determined from the equation 1,        values and δ^(44/40)Ca.    -   2. The depth (“CaCO₃ precipitation depth”) below the surface in        which the precipitation took place, determined from the        δ^(44/40)Ca-values and the equation 2.    -   3. From the borehole depth and the known age of the rock layer,        the subsidence rate can be determined [(drilling depth (m))/(age        of the rock ( ) Ma)=subsidence rate (m/Ma)].

As a result of the procedure one obtains an age depth relationship for arock, just as one would also pursue using mathematical basin modeling.These relationships can now be shown in an empirical age-depthrelationship (empirical model of the basin) (FIG. 5). The proposedvalues according to our process now allow a validation of the values ofthe basin model based on theoretical assumptions and on seismicprofiles. Ideally, the values determined from our method match thevalues from the basin modeling. In this case, the basin model isreliable.

In the case of discrepancy, when empirical and theoretical values do notmatch, the assumptions on which the basin model is based must bereviewed and, if necessary, changed, so that both approaches can bebrought into agreement (“calibration of the basin model”). From thisthere may result in a change of the prediction for the location of theoil-bearing layers and a corresponding adjustment to the desireddrilling depth.

The subsidence of the rocks after they have left the earth's surface isnot usually linear and can only be reconstructed on complex mathematicalbasin models within certain ranges. The comparison of the theoreticallydetermined age—depth relationship of a particular basin with theage—depth relationship values determined by our method then givesimportant clues to the linearity of the reduction. For largerdeviations, it must then be assumed that there was a non-linearity ofthe subsidence or wrong model approaches. In any case in the latter casethe revision of the underlying mathematical model is required.

The comparison of the introduced mathematical model of the basin withempirical age—depth relationships and/or to calibrate increases thereliability of basin models, increases the hit probability ofoil-bearing layers and saves drilling costs.

Further advantages and features of the invention will become apparentfrom the following description of a preferred embodiment with referenceto the accompanying drawings, In the drawings:

FIG. 1 shows the dependence of Δ^(44/40)Ca_(CC) values as a function ofdepth (left axis) and temperature (right axis) of the Ca isotope ratio.

FIG. 2 shows a ⁸⁷Sr/⁸⁶Sr curve of Phanerozoic seawater. By determiningthe ⁸⁷Sr/⁸⁶Sr value of calcite (CC) the age of the parent solution (BS)can be determined.

FIG. 3 shows the δ^(44/40)Ca_(BS)-curve for the Phanerozoic seawater,Using the age determined from the ⁸⁷Sr/⁸⁶Sr-curve, now theδ^(44/40)Ca_(BS)-value necessary for computation van be determined.

FIG. 4 shows the temperature values (° C.) determined according to theinvention from Table 1 as a function of their depth. The symbolscorrespond to very specific drill sites. The arrows in therepresentation mark respectively the average precipitation temperaturesfor the various symbols or locations. Together with the data points ofdifferent locations, the thermal gradient is illustrated.

FIG. 5 shows an example of an inventive determined empirical age-depthrelationship (empirically developed model of the basin) from themeasured values. From the empirically determined fixed point, thenon-linearity of the subsidence rate can be clearly seen.

In FIG. 1 it is assumed that at the earth surface (depth=0 m), atemperature of 15° C. prevails. The corresponding isotope value reflectsthe value of the Δ^(44/40)Ca_(CC) which calcium carbonate precipitatedfrom Jurassic sea water would assume at a temperature of 15° C.

The increase in Δ_(44/40)Ca_(CC) a values adopted here reflects thegeogenic temperature with an increase of 0.033° C./m. AΔ^(44/40)Ca_(CC)=0 is assumed at a temperature of 73° C. and anassociated depth of 1750 m. Information beyond are no longer possiblebecause the Δ^(44/40)Ca_(cc)-value cannot be positive.

The invention will now be illustrated by the following examples with theunderstanding that the universality of this teaching is not limitedthereby.

A calcium carbonate sample taken at 700 m depth yielded, for example,the following results:

Sampling: Sampling is carried out on the drilled rock, usually a pieceof drill core. We are looking for core segments where the porosity isreduced by incorporating recognizable white calcium carbonate. From thismaterial, using a hammer, or better yet a cutter or hollow drill, abetter piece of the rock, about 5 cm³, is separated from the drill core.This hand rock sample is documented. A part of the h hand rock sample ispulverized, and an X-ray diffraction is carried out to determine thepercentage of calcium carbonate as well as the polymorphism, and also,whether the calcium carbonate is present as calcite or aragonite. Afterthis work, the calcium carbonate is dissolved out with a weak acid, forexample, formic acid or 2 N HNO₃. The acid will be weak, so that nocalcium is extracted from the non-calcium carbonate host rock, i.e., itis made sure that the original calcium isotopic composition of theprecipitated calcium carbonate in the rock can be measured.

Measurement: The ⁴⁴Ca/⁴⁰Ca-isotope ratio is determined by massspectrometry using either the thermal ionization- or plasma-massspectrometry. In the case of thermal ionization mass spectrometry, a Caspike of known isotopic composition must be introduced into the solutionbefore the measurement, in order after measuring to calculate out themass discrimination during thermal ionization mass spectrometry.

In the plasma-mass spectrometry likewise a spike can also be added to inorder to increase the precision of the measurement. The measurement canalso be performed using the plasma mass spectrometer by means of theso-called “bracketing standard method”, in which the correction for themass discrimination in the plasma mass spectrometer is carried out bynormalization to a standard known isotopic composition. The peculiarfeature of plasma mass spectrometry of calcium is that you cannotmeasure the ⁴⁴Ca/⁴⁰Ca ratio directly as a rule, as there is an isobareffect with ⁴⁰Ar, which functions as a carrier gas in the unit. In orderto arrive at values therefore first the ⁴²Ca/⁴⁴Ca-relationship ismeasured and then converted to the ⁴⁴Ca/⁴⁰Ca ratio.

In general, the method provides a slightly better thermionic precisionthan the plasma process, however, sample throughput in the plasmaprocess is higher.

In Table 1 an example of an (EXCEL)-based data analysis for thecalculation of precipitation temperatures using the Ca-isotope values(δ^(44/40)Ca) can be seen.

TABLE 1 1 2 3 4 5 6 δ^(44/40)Ca stat. error δ^(44/40)Ca T δ_(44/40Ca) (°C.) stat. error Sample (o/oo) (o/oo) (o/oo) (° C.) (° C.) 1 0.63 0.12−0.52 47 9 2 0.97 0.27 −0.18 64 18 3 0.85 0.08 −0.3 58 5 4 0.84 0.09−0.31 58 6 5 0.7 0.21 −0.45 51 15 6 1.06 0.16 −0.09 69 10 7 1.32 0.190.17 82 12 8 0.88 0.17 −0.27 60 11 9 0.67 0.33 −0.48 49 24 10 1.14 0.16−0.01 73 10 11 1.75 0.07 0.6 103 4 12 1.31 0.22 0.16 81 14 13 1.13 0.08−0.02 72 5 Seawater value: 1.15

Column 1 contains the sample number. Column 2 contains the measured Caisotope value (δ^(44/40)Ca) and column 3 the associated statisticalmeasurement error. In column 4 there is δ^(44/40)Ca, which results fromthe subtraction of the values in column 3 and the seawater value, whichis determined from the age of the solution. the age of the solution,usually seawater, is determined from their ⁸⁷Sr/⁸⁶Sr-Isotopic yields. Incolumn 5, the precipitation temperature in ° C. is then calculated (Tδ^(44/40Ca)(° C.)) from the values of column 4 and Equation 1. Thestatistical error for the temperature in column 6 is determined from thevalues in columns 3, 4 and 5.T(° C.)=(Δ^(44/40)Ca+1.46)/0.02  (1)

In FIG. 4, the calculated temperature values (in ° C.) of Table 1 arenow shown as a function of their depth. The symbols represent veryspecific drill sites. The arrows in the figure indicate the averageprecipitation temperatures for the various symbols or locations.Together with the data points of different locations, the thermalgradient (equation 2) is also shown.T _(geogenic)=15° C.+(0.033° C./m)*Depth(m)  (2)

FIG. 4 shows that the precipitation temperatures (° C.), as determinedusing the measured Ca isotope ratios, do not coincide with the values ofthe geogenic temperature gradient (broken line) and indicate too great adepth relative to the temperature. The latter is due to the fact thatthe carbonates precipitated at an earlier date which corresponds to thedepth, but were later displaced by a more accelerated subsiding to agreater depth.

From FIG. 4 it can be seen that the precipitation temperatures (Tδ_(44/40Ca)) assume a higher depth at the same temperature. Thereby alarge number of measurements at a depth of about 2500 m show atemperature of ˜50° C. The geogenic temperature gradient already showsbetween ˜1500 m a temperature of ˜50° C. In contrast, a temperature of˜90° C. would be expected at ˜2500 m.

This apparent discrepancy is based thereon, that the carbonates havebeen precipitated at an earlier time, namely, when the rock,corresponding to the geologic deposit, was at a depth of ˜1500 m. Sincethe precipitation of carbonates is always associated with the maturationof petroleum, this depth, or rather the associated age, marks thebeginning of the oil migration into the reservoir rock.

The age and subsidence history can be calculated from the⁸⁷Sr/⁸⁶Sr-relationship. Here, in the specific case, the measured⁸⁷Sr/⁸⁶Sr-relationship of the host rock is ˜0.7075 which corresponds toa geologic age of ˜190 Ma. From the known present-day drilling depth of˜2500 m, an average subsidence rate of ˜13 m/Ma (2500 m/190 Ma) can becalculated. From the precipitation depth of ˜1500 m, there results atime of precipitation of ˜115 Ma. These relationships can now be shownin an empirical age-depth relationship (empirically developed basin mod&FIG. 5).

This basin model determined empirically using the measured Ca and Srisotopic ratios can be now compared with the basin model based ontheoretical assumptions and seismic profiles. Ideally the results match,in the case of discrepancy a calibration of the theoretical model can becarried out on the basis of the empirical model of the basin.

LIST OF REFERENCE NUMERALS

-   A age-   D depth, drilling depth-   G geothermal gradient-   T temperature-   xx rock position (0.033° C./m)-   x1 rock position on the surface-   x2 rock position at approximate timing and depth of the CaCO3    precipitation-   x3 rock position today

The invention claimed is:
 1. A method for validating or calibrating asedimentary basin model by determining an age depth relationship, themethod comprising: obtaining a mathematical model of a sedimentary basinplotting the age-depth relationship of rocks to be validated orcalibrated, i. obtaining a porous sample of sedimentary rock from apredetermined depth, the sedimentary rock including calcite, ii.determining the geologic age of the sedimentary rock, iii. dissolvingcalcite from the sample of the sedimentary rock using a dilute acid, iv.determining a Ca isotope ratio of two different Ca isotopes, v.determining the age of a solution in the sedimentary rock by determininga Sr-isotope ratio of ⁸⁷Sr/⁸⁶Sr and referencing this ratio withavailable data regarding the relationship between age and ratio of⁸⁷Sr/⁸⁶Sr, vi. determining the Ca isotopic ratio of a Bulk Solution byreferencing the age of v. with known correlations or measuring the Caisotopic ratio using Phanerozoic seawater from the pores of the sampleof the sedimentary rock, vii. calculating the difference between the Caisotope ratio step iv and step vi, viii. determining theCaCO₃-precipitation temperature (Tprecipitation) using the differencecalculated in step vii by referencing with available data [p. 3/4], ix.determining CaCO₃ precipitation depth for the determination of the fixedpoint in its depth position X(m) in which the CaCO₃ has precipitatedfrom a parent solution at known geothermic gradient, and x. using theproduct of step ix to validate or calibrate the basin model.
 2. Themethod according to claim 1, wherein the ratio of Ca isotopes ⁴⁰Ca and⁴⁴Ca (⁴⁴Ca/⁴⁰Ca) is used for determining an isotopic ratio of theprecipitated CaCO₃ (CC).
 3. A method according to claim 1, wherein acalculation of an Ca-isotopic difference (Δ^(44/40)Ca) between ageological known solution (BS) and that CaCO₃ (CC), precipitated fromthe solution, is based on(Δ^(44/40)Ca=δ^(44/40)Ca_(CC)−δ^(44/40)Ca_(BS)) at a known δ^(44/40)Ca_(BS).
 4. The method according to claim 1, wherein in the case of anunknown δ^(44/40) Ca_(BS) a separation of the strontium ions (Sr²⁺) inthe solution, recovered from the precipitated calcium carbonate bydissolving out of sedimentary rocks by dilute acids, is carried out viaion chromatography, a Sr-isotope ratio ⁸⁷Sr/⁸⁶Sr is determined for thetwo Sr-isotopes ⁸⁷Sr and ⁸⁶Sr, and a determination of the Ca isotopicdifference is carried out by comparing the determined Sr-isotope ratiowith a known Sr-isotope ratio of Phanerozoic seawater.
 5. The methodaccording to claim 1, wherein the determination of theCaCO₃-precipitation temperature is based on the relationshipΔ^(44/40)Ca(‰)=0:02 (‰/° C.)*Temperature(° C.)−1.46‰ according to thefollowing equation 1: $\begin{matrix}{{T\left( {{^\circ}\;{C.}} \right)} = {\frac{{\Delta^{44/40}{Ca}} + 1.46}{0.02}\;.}} & {{Equation}\mspace{14mu} 1}\end{matrix}$
 6. The method according to claim 1, wherein thedetermination of the CaCO₃ precipitation depth (X(m)) occurs accordingto the following Equation 2: $\begin{matrix}{{X(m)} = {\frac{{\delta^{44/40}{Ca}_{CC}} - {\delta^{44/40}{Ca}_{BS}} + 1.16}{0.00066}\;.}} & {{Equation}\mspace{14mu} 2}\end{matrix}$
 7. The method according to claim 1, wherein the actualtemperature gradient or distribution is detected by a direct temperaturemeasurements in the borehole from which the sample is taken.